Overview

This section provides an introduction to the options available to
you when developing a PHP application that needs to interact with a
MySQL database.

What is an API?

An Application Programming Interface, or API, defines the classes,
methods, functions and variables that your application will need to
call in order to carry out its desired task. In the case of PHP
applications that need to communicate with databases the necessary
APIs are usually exposed via PHP extensions.

APIs can be procedural or object-oriented. With a procedural API you
call functions to carry out tasks, with the object-oriented API you
instantiate classes and then call methods on the resulting objects.
Of the two the latter is usually the preferred interface, as it is
more modern and leads to better organized code.

When writing PHP applications that need to connect to the MySQL
server there are several API options available. This document
discusses what is available and how to select the best solution for
your application.

What is a Connector?

In the MySQL documentation, the term connector
refers to a piece of software that allows your application to
connect to the MySQL database server. MySQL provides connectors for
a variety of languages, including PHP.

If your PHP application needs to communicate with a database server
you will need to write PHP code to perform such activities as
connecting to the database server, querying the database and other
database-related functions. Software is required to provide the API
that your PHP application will use, and also handle the
communication between your application and the database server,
possibly using other intermediate libraries where necessary. This
software is known generically as a connector, as it allows your
application to connect to a database server.

What is a Driver?

A driver is a piece of software designed to communicate with a
specific type of database server. The driver may also call a
library, such as the MySQL Client Library or the MySQL Native
Driver. These libraries implement the low-level protocol used to
communicate with the MySQL database server.

By way of an example, the PHP
Data Objects (PDO) database abstraction layer may use one of
several database-specific drivers. One of the drivers it has
available is the PDO MYSQL driver, which allows it to interface with
the MySQL server.

Sometimes people use the terms connector and driver interchangeably,
this can be confusing. In the MySQL-related documentation the term
"driver" is reserved for software that provides
the database-specific part of a connector package.

What is an Extension?

In the PHP documentation you will come across another term -
extension. The PHP code consists of a core,
with optional extensions to the core functionality. PHP's
MySQL-related extensions, such as the mysqli
extension, and the mysql extension, are
implemented using the PHP extension framework.

An extension typically exposes an API to the PHP programmer, to
allow its facilities to be used programmatically. However, some
extensions which use the PHP extension framework do not expose an
API to the PHP programmer.

The PDO MySQL driver extension, for example, does not expose an API
to the PHP programmer, but provides an interface to the PDO layer
above it.

The terms API and extension should not be taken to mean the same
thing, as an extension may not necessarily expose an API to the
programmer.

What are the main PHP API offerings for using
MySQL?

There are three main API options when considering connecting to a
MySQL database server:

PHP's MySQL Extension

PHP's mysqli Extension

PHP Data Objects (PDO)

Each has its own advantages and disadvantages. The following
discussion aims to give a brief introduction to the key aspects of
each API.

What is PHP's MySQL Extension?

This is the original extension designed to allow you to develop PHP
applications that interact with a MySQL database. The
mysql extension provides a procedural interface
and is intended for use only with MySQL versions older than 4.1.3.
This extension can be used with versions of MySQL 4.1.3 or newer,
but not all of the latest MySQL server features will be available.

Note:

If you are using MySQL versions 4.1.3 or later it is
strongly recommended that you use the
mysqli extension instead.

The mysql extension source code is located in the
PHP extension directory ext/mysql.

The mysqli extension, or as it is sometimes
known, the MySQL improved extension, was
developed to take advantage of new features found in MySQL systems
versions 4.1.3 and newer. The mysqli extension is
included with PHP versions 5 and later.

The mysqli extension has a number of benefits,
the key enhancements over the mysql extension
being:

Object-oriented interface

Support for Prepared Statements

Support for Multiple Statements

Support for Transactions

Enhanced debugging capabilities

Embedded server support

Note:

If you are using MySQL versions 4.1.3 or later it is
strongly recommended that you use this
extension.

As well as the object-oriented interface the extension also provides
a procedural interface.

The mysqli extension is built using the PHP
extension framework, its source code is located in the directory
ext/mysqli.

PHP Data Objects, or PDO, is a database abstraction layer
specifically for PHP applications. PDO provides a consistent API for
your PHP application regardless of the type of database server your
application will connect to. In theory, if you are using the PDO
API, you could switch the database server you used, from say
Firebird to MySQL, and only need to make minor changes to your PHP
code.

Other examples of database abstraction layers include JDBC for Java
applications and DBI for Perl.

While PDO has its advantages, such as a clean, simple, portable API,
its main disadvantage is that it doesn't allow you to use all of the
advanced features that are available in the latest versions of MySQL
server. For example, PDO does not allow you to use MySQL's support
for Multiple Statements.

PDO is implemented using the PHP extension framework, its source
code is located in the directory ext/pdo.

The PDO MYSQL driver is not an API as such, at least from the PHP
programmer's perspective. In fact the PDO MYSQL driver sits in the
layer below PDO itself and provides MySQL-specific functionality.
The programmer still calls the PDO API, but PDO uses the PDO MYSQL
driver to carry out communication with the MySQL server.

The PDO MYSQL driver is one of several available PDO drivers. Other
PDO drivers available include those for the Firebird and PostgreSQL
database servers.

The PDO MYSQL driver is implemented using the PHP extension
framework. Its source code is located in the directory
ext/pdo_mysql. It does not expose an API to the
PHP programmer.

In order to communicate with the MySQL database server the
mysql extension, mysqli and
the PDO MYSQL driver each use a low-level library that implements
the required protocol. In the past, the only available library was
the MySQL Client Library, otherwise known as
libmysqlclient.

However, the interface presented by libmysqlclient was
not optimized for communication with PHP applications, as
libmysqlclient was originally designed with C
applications in mind. For this reason the MySQL Native Driver,
mysqlnd, was developed as an alternative to
libmysqlclient for PHP applications.

The mysql extension, the
mysqli extension and the PDO MySQL driver can
each be individually configured to use either
libmysqlclient or mysqlnd. As
mysqlnd is designed specifically to be utilised
in the PHP system it has numerous memory and speed enhancements over
libmysqlclient. You are strongly encouraged to take
advantage of these improvements.

Note:

The MySQL Native Driver can only be used with MySQL server
versions 4.1.3 and later.

The MySQL Native Driver is implemented using the PHP extension
framework. The source code is located in
ext/mysqlnd. It does not expose an API to the
PHP programmer.

Comparison of Features

The following table compares the functionality of the three main
methods of connecting to MySQL from PHP:

mysqli can be great in some circumstances but much work has been put into PHP Portable Data Objects (PDO) which you should also consider when choosing a way to connect to your database using php. For example, PDO supports MySQL with minimal performance hit and the code your write for it will support many other databases with little or no changes. That said, the database connection code, even if you have to change a lot of it to use another database will be much less work than coding your actual database data entry and report apps. When I started creating PHP/MySQL apps years ago, I used php's native support for PHP then moved to PEAR:DB and MDB/MDB2 and finally to wizzyweb which is basically like "phpMyAdmin for Apps" to create apps as it automatically generates the PHP PDO connection code and the application code. Sure, I could code it all from scratch but I save about 90% of the time it used to take. The point is look at the total amount of time you will save by using native code vs. an abstraction layer. Most people find that programmer time is the most valuable part of the equation so anything than can save programmer time should be heavily weighted.